1. Field of the Invention
This invention relates to power supplies, and more particularly relates to adaptively increasing the efficiency of a switching power supply.
2. Description of the Related Art
A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electrical or other types of energy to an output load or group of loads. A power supply, in some embodiments may be configured to convert power in one form to another form, such as converting AC power to DC power. The regulation of power supplies is typically done by incorporating feedback and control circuitry to tightly control the output voltage or current of the power supply to a specific value. The specific value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input. A switching power supply is a power supply that incorporates a switching regulator that typically switches a power transistor, usually a metal-oxide-semiconductor field-effect transistor (“MOSFET”), between saturation and cutoff with a controller to maintain a constant output voltage.
For example, in an electrical device such as a computer, a switching power supply is typically designed to convert an AC input voltage, such as is traditionally provided by a conventional wall socket, into one or more low-voltage DC power outputs for transmission to internal components of the device. Conversion is sometimes performed in stages that may include different power supply topologies such as a rectification stage, a boost stage, buck stage, or other topology.
In some instances, the switching power supply may also incorporate circuitry to perform active power factor correction. Active power factor correction is typically performed in a boost converter that substantially maintains a constant DC bus voltage on its output while drawing a current that is in phase with and at the same frequency as the line voltage.
Additional stages in the power supply may utilize the DC bus voltage provided by the boost converter to produce desired output voltages for use by electronic devices. A typical boost converter with active power factor correction might regulate the DC bus voltage to substantially mirror a set reference voltage or set point of about 400 Volts. However, in a typical switching power supply this may result in an efficiency of less than 80% when operating at a 20% load. This is significant because the Environmental Protection Agency requires that in order to be compliant with energy consumption regulations, a switching power supply must operate at least above 80% efficiency when operating at 20% of the full load capacity of the switching power supply.
Conventional art addresses this problem by utilizing expensive devices and magnetics to meet the efficiency requirements. However, none of the conventional art currently available has provided a cost effective means for satisfactorily meeting efficiency requirements when operating at lower loads. Thus, there is a need for an adaptive low-cost switching power supply with improved efficiency at relatively low loads.